Plug-type lag fuse



May 11, 1954 L. N. BAr-:NzlGER 2,678,363

PLUG-TYPE LAG FUSE Filed May'l, 1952 HIGH MELTING OOHJT' (.OUJ MELTIMG' POINT Patented May 11, 1 954 l f fi UNITED' STATES PATENT OFFICE PLUG-TYPE LAG FUSE Leonard N. Baenziger, Pawtucket, R. I., assignor to Royal Electric Company, Inc., Pawtucket, R. I., a corporation of Rhode Island Application May 1, 1952, serial No. 285,371

s claims. (c1. zou- 123) This invention relates to plug-type lag fuses, and is an improvement on the lag fuse disclosed in my Patent No. 2,557,587, dated June 19, 1951.

The principal purpose of the present invention is to provide an improved plug fuse of conventional exterior form but equipped with a fuse link having heat absorbing bodies of predetermined and substantially equal mass disposed on opposite sides of the neck or fusible portion of the link, whereby the heat caused by a moderate and brief overload will be dissipated without melting the fusible link, yet the fuse will blow under a sustained overload or a short circuit.

The fuse of my prior patent operates with general satisfaction in performing the same purpose, but the formation of heat-absorbing solder pockets by coiling a continuous fuse strip upon itself does not ensure accurately predetermined masses and uniform blowing time under overloads of the circuit. Hence, in accordance with this improvement, the pockets for the solder masses are accurately and uniformly produced by bending the fuse link in dies to provide a pair of preformed pockets of similar shape, each of which will hold a predetermined mass of heatabsorbing material. The fuses thus made will accordingly exhibit a uniform time delay period under temporary and moderately overloads.

A further object of this invention is to provide a fuse link composed of two metals of different conductivity whereby a relatively high resistance and low melting point metal such as zinc may be used for the fusible leg of the composite strip, and a metal of lower electrical resistance, such as brass, may be used for the other leg, to prolong the time lag before the link blows. Thus, the overload rating of the improved fuse may be regulated by varying the thickness of either or both legs, while maintaining constant the total mass of heat-absorbing solder plugs formed in the respective legs.

A preferred embodiment of the invention is illustrated in the accompanying drawings, in which:

Fig. 1 is a plan view of the improved lag fuse, partly broken away and in section;

Fig. 2 is a section on line 2-2 of Fig. 1; and Fig. 3 is an edge view of the respective legs of the fuse link, with the solder pockets formed therein, and with the legs associated in operative relation.

In the particular form chosen for the purpose of illustration, the plug-type lag fuse comprises the usual body II of insulating material, a conventional top part or cover I2 of glass or the which holds the body and cover in assembled relation and which constitutes a conductor when the'plug is screwed into a conventional socket. The base terminal I4 is riveted in the exposed end of the body II in the customary manner. The structural details of these parts of the fuse are not material to this invention, and may be varied as desired.

In accordance with this invention, the improved fuse link preferably consists of a zinc strip or leg l5 wrapped around the endof the tubular portion I E of the cover I2 and having one end soldered at Il to the shell I3; and a brass strip or leg I3 soldered or otherwise attached at one end to the terminal I4. The opposite end portion of the zinc leg I5 is bent to form a substantially rectangular, open-sided pocket I9, and may be further bent at 20 to provide a narrow fusible neck 2| disposed approximately at the transverse center of the fuse cavity. The eX- tremity 22 of leg I5 is attached to the brass leg I8 as explained below.

The opposite end of the brass strip I8 is bent to form a three-sided, substantially rectangular pocket 23 of a size approximately corresponding to the pocket I9. The extreme end 22 of the zinc leg is mechanically and electrically connected to the extremity 24 of the brass leg, and may extend outwardly to close the pocket 23, as shown in Fig. 2.

It is not essential that the pockets I9 and 23 be identical in size, but the two pockets are accurately formed, preferably by dies, to ensure that the total capacity of both pockets may be predetermined. These pockets receive a massI of heat-absorbing material, preferably solder which hardens in the respective pockets I9 and 23 as solder plugs 25 and 26. Plug 26 serves as the connecting means between leg ends 22 and 24. By forming the pockets as just described, the total mass of the two lugs will be uniform in every lag fuse produced pursuant to this invention.

It will be apparent that the solder plugs will absorb and dissipate the heat of a quick surge of current caused by a moderate overload, so that the fusible neck 2| will not melt under such conditions; but that the fuse link will blow in case of a sustained or heavy overload, or of a short circuit. It will also be understood that the operating overload time may be regulated, in part, by varying the thickness of either or both of the fuse strips I5 and I8, while maintaining the same width thereof and also maintaining the 3 same capacity of the respective solder pockets i9 and 23.

I claim:

1. A plug-type lag fuse comprising a fuse link composed of two metal strips of differing melting points means electrically connecting said strips together in series, each strip having a three-sided Vpocket Vof predetermined capacity formed therein, the strip of lower melting point having a tusible portion, and solder plugs of size corresponding to the `capacities of the respective pockets received and held in the respective pockets.

2. A plug-type lag fuse comprising a fuse link composed of two metal strips'of diii'eringrnelting points means electrically connecting said strips together in series. each strip having a three-sided pocket of predetermined capacity formed therein, the strip of lower melting point having a fusible portion, and solder plugs of size corresponding to the capacities of the respective pockets received and held in the respective pockets, one end of said fusible strip closing the open end of the pocket in the other strip and being connected to vsaid other strip by the solder in said pocket.

`size corresponding to the capacities of the respective pockets, received and held in the respective pockets, the plug in said second pocket being connected to said `leg and forming an electrical connection between said strips.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,379,436 Baxter May 24, 1921 2,224,111 Wood Dec. 3, 1940 2,286,518 Taylor June 16, .1942 2,557,926 Swain et al. June 26, 1951 

